1. Field of the Invention
The present invention generally relates to a brushless DC motor, and more particularly relates to a brushless DC motor which includes a rotation-control portion for controlling the rotation of the motor based on data stored in memory and a driving circuit for providing driving current controlled by the rotation-control portion.
2. Description of the Related Art
Brushless DC motors are used for various applications such as office electronics, home electronics, and car electronics. In some applications, the rotation of such brushless DC motors needs to be controlled with great accuracy.
The rotation-control portion of the brushless DC motor may be equipped with an IC having an integrated micro computer. Generally, the micro computers have embedded memories, and the micro computer used for the rotation-control portion includes a control program which regulates the driving current supplied to a stator based on a rotational state of the motor, temperature, and external signals. The rotation of the motor including such a rotation-control portion can be more sophisticatedly controlled compared to motors without such control portions.
Conventionally, a read-only nonvolatile memory (ROM) is used for the embedded memory of the micro computer. The control program such as a feedback control program is stored in the ROM of the micro computer. Then, the micro computer with the ROM is mounted on a circuit board which is to be installed onto the brushless DC motor.
The rotational setting of such a brushless DC motor can be variously modified by modifying the control program installed in the ROM.
Generally, two kinds of memories are used for the embedded memories of the micro computers; a one time programmable read only memory (an OTP-ROM) and an electrically erasable programmable ROM (an EEP-ROM or a flash memory). The OTP-ROM is inexpensive compared to the flash memory, therefore the micro computer with the OTP-ROM (OTP micro computer) is generally used for products in mass-production. However, when the design or configuration of the product is changed, the OTP micro computer on the motor needs to be replaced because the program stored on the OTP-ROM cannot be modified. If the micro computer has been already mounted on the circuit board, or the circuit board with the micro computer has been already installed onto the motor, replacing the micro computer will be a burdensome and time-consuming task, which greatly affects the efficiency of manufacturing the motor. Moreover, the replaced OTP micro computer needs to be discarded or stored so as to reuse them for other product models, which makes the efficiency of manufacturing the motor even less. The OTP micro computer is inexpensive itself, but as a result of the burdensome and time-consuming task mentioned above, the conventional brushless DC motor with the OTP micro computer is expensive and requires more time for its production.
In designing the control portion of the motor, ROM data of the motor is frequently required, and the brushless DC motor equipped with the micro computer in which access to the embedded memory of the micro computer during or after the manufacturing thereof is in demand. However, the circuit board is generally attached to the inside of the brushless DC motor, and it is generally inaccessible from outside of the motor.